The present application relates generally to control systems for machines with electronically controlled hydrostatic transmissions. The present application relates more specifically to a straight tracking control system for a machine having a dual path electronically controlled hydrostatic transmission.
One type of machine with a dual path electronically controlled hydrostatic transmission can be a crawler-tractor such as a bulldozer. “Bulldozers” or “dozers,” as those terms may be used herein, refer to crawler-tractors that are equipped with a blade for scraping the ground or pushing material along the ground. The blade is pivotally connected to the crawler-tractor chassis such that it can pivot up and down. Blade controls are provided to the operator in the cab of the vehicle to permit the operator to raise and lower the blade with respect to the chassis of the crawler-tractor. One of the most common uses for blades on bulldozers is to level or otherwise contour the ground for the construction of houses, buildings, parking lots, and roads. During the process of leveling or contouring the ground, the operator of the bulldozer may want to travel in a straight direction for a variety of reasons such as efficiency and simplicity.
The bulldozer can have a dual path electronically controlled hydrostatic transmission or ground drive system that is used for the propulsion and steering of the bulldozer. Machines with a dual path electronically controlled hydrostatic transmission, such as the bulldozer or other crawler-tractor, can have an independent pump and motor to drive each of the left side and the right side of the machine's driveline or a single pump to control motors on each of the left and right side of the machine's driveline. At times, the pump and/or motor displacement on each side of the driveline can vary in an unpredictable manner due to various reasons, including manufacturing tolerances, hydraulic driveline inefficiencies, “wear and tear” of the pump and motor components, loading conditions, etc., that can result in non-straight, i.e., curved or angled, movement of the machine when the machine is commanded or steered in a straight direction.
Therefore, what is needed is a control system for machines with dual path electronically controlled hydrostatic transmissions that can maintain a straight direction of travel for the machine when commended straight by an operator driving the machine.